1. Field of the Invention
This invention relates to a lighting unit that is preferably used when a product inspection is conducted by means of reflected light from the lightning unit.
2. Discussion of the Relevant Art
As a method of examining the surface of a product, it has generally been known that a product to be examined is irradiated on its upper side by a lighting unit having an illuminant assembly on its underside, with the reflected light then being visually inspected or photographed in close proximity to the lighting unit. If there is some unevenness in light intensity on the surface to be examined, it may be that a micro flaw or finishing defect on the surface of the product to be examined has failed to be detected. Therefore, in examining a surface of a product it is very common to use a lighting unit having an illuminant assembly of such a construction that the assembly has a plurality of illuminants such as light-emitting diodes positioned all over the underside of the lighting unit, with the entire underside thereof emitting light so as to maintain an even light intensity on the surface to be examined.
However, if a lighting unit has the above construction, a plurality of illuminants must be positioned all over the underside of the lighting unit, greatly increasing the time required to assemble the lighting unit. This not only causes some unevenness in light intensity on the surface to be examined, but also requires precision in assembly of the lighting unit to prevent said unevenness from being caused by unevenness in the assembly orientation of each illuminant. In addition, if the surface to be examined is glossy, the illuminants are reflected, making it impossible to inspect the surface.
It is an object of the present invention to provide a lighting unit characterized by the fact that the lighting unit having a smaller number of illuminants can reduce unevenness in light intensity on a surface of a product to be examined, and by the fact that the illuminants can be set up easily.